Patent document EP 0 565 153 A1 discusses a train monitoring system. The train monitoring system has a plunger device including a cavity which may be filled with a fluid and which is delimited by a plunger which is displaceable along a displacement axis. It is supposed to be possible to increase a brake pressure present in at least one wheel brake caliper by transferring a brake fluid volume from the cavity to the at least one wheel brake caliper by displacing the plunger.